The present invention relates to a specimen manipulating mechanism effectively used in a charged-particle beam instrument, such as Auger electron spectrometer or ion scanning microscope, that requires an ultrahigh vacuum to examine the surface of a specimen.
A conventional charged-particle beam instrument such as a scanning electron microscope has a specimen manipulating mechanism in its specimen chamber as shown schematically in FIG. 1. This manipulating mechanism is comprised of a mechanism for translating a specimen in the direction of Z axis coincident with the optical axis of the electron beam and also in the directions of the X and Y axes perpendicular to the Z axis, a mechanism for rotating the specimen about the Z axis, and a mechanism for tilting the specimen with respect to the X or Y axis. Referring specifically to FIG. 1, the specimen chamber of the scanning electron microscope is indicated by reference numeral 1. An electron-optical column 2 including objective lenses is mounted on the chamber that has a front cover or wall 3 to which a specimen tilt stage 4 is held so as to be rotatable about the Y axis. A toothed wheel 5 is secured to the tilt stage, and is in mesh with a toothed wheel 6 that is connected via a shaft 7 to a knob 8 disposed on the atmospheric side of the front cover. Since rotation of the knob 8 turns the stage 4 about the Y axis, the specimen can be tilted at any desired angle. A Y-axis stage 10 for movement along the Y axis, an X-axis stage 11 for movement about the X axis, and a rotary stage 12 are stacked on the tilt stage 4. A specimen holder 14 that holds a specimen 13 is inserted into the rotary stage. A plurality of balls are placed between the tilt stage 4 and the Y-axis stage 10 and also between the Y-axis stage 10 and the X-axis stage 11 to make the movement of each stage smooth. The shaft 15 of the rotary stage extends downwardly through the translational stages 10 and 11. A bevel gear 16 is securely fixed to the lower end of the shaft 15, and meshes with a bevel gear 17 which is connected via a universal joint 18 and a shaft 19 to a knob 20 mounted to the front cover 3. The rotating shaft 15 takes the form of a hollow tubing, into which a shaft 21 for vertically moving the specimen is inserted. The lower end of the shaft 21 bears on a lever 22 which, when rotated, acts to move the specimen holder 14 vertically. The lever 22 is connected to a knob 26 via a threaded rod 23, a universal joint 24, and a shaft 25. A knob 27 is connected to the Y-axis stage 10 via a shaft 28, a universal joint 29, and a threaded rod 30 such that the rotation of the knob 27 is transmitted to the stage 10 as a translational motion. Indicated by reference numeral 9 is a knob for manipulating the X-axis stage. (The linkage between knob 9 and the X-axis stage is not shown in the drawing but can be understood as like the linkage between knob 27 and the Y-axis stage.)
In the conventional apparatus constructed as described above, if the knobs 9 and 27 are rotated, the specimen 13 is translated in the directions of the X and Y axes in a plane perpendicular to the optical axis Z. If the knob 26 is rotated, the specimen is shifted in the direction of the optical axis. If the knob 20 is rotated, the specimen rotates about the axis of the shaft 16. If the knob 8 is turned, the tilt stage 4 is angularly moved thus to rotate all the stages about the Y axis, whereby the sample is tilted to a desired angular position. Accordingly, this configuration permits the specimen to be moved to any desired position or tilted in any spatial attitude relative to the electron beam, thus enabling observation of the specimen from any desired position or angle. However, if the specimen is inclined at a large angle, the four driving shafts swing and come close to one another, imposing limitations on the amounts of the movements of the shafts and on the tiltable range of angle. Another difficulty arises from many O rings that are used as hermetic seals to transmit the rotary motions of the knobs 8, 27, 26, and 9, which are installed on the front cover for moving the specimen, to the shafts for driving the stages in the specimen chamber, as can be seen from the figure. That is, these rings release a large quantity of gas and hence it is impossible to maintain the degree of vacuum in the specimen chamber 1 at a sufficiently high value. Another difficulty comes from the numerous threaded rods or the like which are used to transmit the rotations of the shafts in the specimen chamber to the stages. In particular, these feed rods produce large sliding friction and so a lubricant is often employed to minimize this friction. Unfortunately, this lubricant also discharges a large quantity of gas, leading to a deterioration in the degree of vacuum in the specimen chamber 1.
It is known that the analysis of the surface of a specimen can be effected by an Auger electron spectrometer or photoelectron spectrometer. The charged-particle beam instrument of this kind needs a specimen manipulating mechanism for translating or tilting the specimen in any desired manner to make an analysis of a desired region of it. Further, the instrument requires that the space, or the specimen chamber in which a specimen is placed, be maintained at a quite low pressure in order to keep the surface clean for enhancing the accuracy of the analysis. For this reason, a specimen manipulating mechanism as shown in FIG. 1 cannot be used for the instrument necessitating a high vacuum in this way. In addition, the use of a number of O rings as hermetic seals is undesirable for the bakeout of the members mounted in the specimen chamber. Accordingly, it may be suggested to use a rotary motion feedthrough mechanism making use of a metal bellows for an ultrahigh vacuum environment instead of the O rings that serve as the hermetic seals for the rotary members, in order to keep the interior of the chamber in an ultrahigh vacuum condition, but the rotary motion feedthrough mechanism is unable to transmit large torque and is expensive. Further, it occupies a relatively large space. Therefore, if such rotary motion feedthrough mechanisms are used in quantities, the whole specimen manipulating mechanism becomes bulky. Another difficulty is that special lubricants which are suited for ultrahigh vacuum and can be used for the threaded feed rods in general require periodic maintenance, and therefore use of such feed rods in quantities in an instrument requiring an ultrahigh vacuum is undesirable. Consequently, the prior art specimen manipulating mechanism for an Auger electron spectrometer or the like has incorporated a specimen manipulating mechanism which is capable of giving only two movements in the directions of X and Y axes to the specimen unlike the apparatus of FIG. 1 which gives as many as five movements.